Alloy 909 (UNS N19909) is a precipitation-hardenable nickel-iron-cobalt superalloy representing the most advanced generation of low-expansion alloys. With controlled additions of niobium, titanium, and silicon, this grade achieves an optimized balance of low thermal expansion, high strength, and improved notch-rupture ductility, making it the preferred choice for gas turbine components requiring tight clearance control throughout thermal cycles.
1. Product Specifications & Physical DataZYTC Alloy supplies UNS N19909 in mill forms suitable for aerospace fasteners, turbine casings, and precision components requiring certified low-expansion properties and elevated-temperature strength. Available Forms: Round bar, flat bar, sheet, strip, forgings, billet, and welding wire. Specifications: AMS 5718, AMS 5719, AMS 5869 (sheet/strip), UNS N19909.
| Chemical Composition (Weight %) | Alloy 909 Specification |
|---|
| Nickel (Ni) | 36.0 - 40.0 | | Iron (Fe) | Balance (approx. 42% nominal) | | Cobalt (Co) | 12.0 - 14.0 | | Niobium (Nb) | 4.3 - 5.2 | | Titanium (Ti) | 1.3 - 1.8 | | Silicon (Si) | 0.25 - 0.50 | | Aluminum (Al) | ≤ 0.15 | | Carbon (C) | ≤ 0.06 |
Note: Controlled silicon addition improves oxidation resistance and notch-rupture properties compared to earlier low-expansion alloys . | Physical Properties | Metric | Imperial |
|---|
| Density | 8.30 g/cm³ | 0.300 lb/in³ | | Melting Range | 1390 - 1430°C | 2535 - 2605°F | | Thermal Expansion (25-425°C) | 7.0 - 7.7 µm/m·°C | 3.9 - 4.3 µin/in·°F | | Curie Temperature | 425 - 460°C | 797 - 860°F | | Thermal Conductivity | 14.8 W/m·K | 103 BTU·in/hr·ft²·°F |
| Mechanical Properties (Precipitation Hardened) | Metric | Imperial |
|---|
| Tensile Strength | 1300 MPa | 189,000 psi | | Yield Strength (0.2% offset) | 1140 MPa | 165,000 psi | | Elongation at Break | 15% | 15% |
2. Operating Conditions & Selection CriteriaAlloy 909 (UNS N19909) was developed as a successor to Alloys 903 and 907, incorporating metallurgical advances that enhance high-temperature performance while maintaining the low-expansion characteristics critical for modern gas turbine efficiency. Service Temperature Range: Optimized for continuous operation from cryogenic temperatures up to 650°C (1200°F). Silicon addition improves oxidation resistance compared to earlier grades, though protective coatings still recommended above 650°C . Low-Expansion Performance: Coefficient of thermal expansion approximately 7.0-7.7 µm/m·°C through 425°C (797°F), enabling tight clearances in turbine casing, seal, and bolting applications . Notch-Rupture Strength: Silicon modification significantly improves notch ductility compared to Alloys 903 and 907, addressing a critical limitation in threaded fastener applications . Strength Retention: Maintains yield strength above 1000 MPa at 540°C (1000°F); 100-hour rupture strength at 650°C exceeds 550 MPa . Microstructural Stability: Precipitation-hardened by gamma-prime [Ni₃(Nb,Ti)] phase; optimized silicon content stabilizes grain boundaries and improves long-term performance . Oxidation Consideration: Limited chromium content results in oxide scaling above 650°C; specify coatings for extended service in oxidizing environments .
3. Fabrication & Material ComparisonIncoloy 909 represents the culmination of low-expansion superalloy development, offering improved fabricability and service performance compared to predecessor grades. Machining: Best performed in solution-annealed condition. Carbide tooling recommended with positive rake angles. Water-based coolants for high-speed operations. Reduced notch sensitivity improves machinability compared to Alloy 907 . Welding: Good weldability using GTAW, GMAW, SMAW, and submerged-arc processes. Matching filler metal (AMS 5836) recommended. Silicon addition improves weld pool fluidity and reduces hot cracking susceptibility compared to earlier grades . Forming & Heat Treatment: Hot Working Range: 983-1120°C (1800-2050°F) Forging Range: 1060-1122°C (1940-2050°F) Annealing: 983-1010°C (1800-1850°F), air cool or faster Aging Treatment (typical): 718-732°C (1325-1350°F) × 8 hours, furnace cool to 621°C (1150°F), hold 8 hours, air cool Cold Working: Standard tooling acceptable; intermediate anneals may be required for severe deformation
Material Comparison: vs. Alloy 903: Enhanced notch-rupture strength and improved oxidation resistance through silicon addition; preferred for high-temperature fastener applications . vs. Alloy 907: Better long-term thermal stability and fabricability; represents the preferred specification for new designs requiring low-expansion properties . vs. Inconel 718: Significantly lower thermal expansion (approximately 50% reduction); selected where clearance control outweighs absolute oxidation resistance requirements . vs. Stainless Steels: Orders of magnitude higher strength with controlled expansion; enables designs impossible with conventional austenitic materials .
Applications Gas turbine engine casings and shrouds High-temperature bolting (steam turbine, gas turbine) Turbine seals and seal supports Rocket engine thrust chambers Ordnance hardware and precision instruments Glass-to-metal seals High-temperature springs requiring dimensional stability
Contact ZYTC Alloy for certified Alloy 909 materials with complete traceability, AMS specifications, technical datasheets, and competitive pricing on standard sizes or custom-forged components. Email:daisy@zytcsteel.com WhatsApp/WeChat: +86 17335753350 |
